When Windows stops recognizing a previously functioning hard drive, the damage is either to physical to the drive or the result of logical damage to the file system. If you removed the drive without ejecting it first, that procedure may have caused partition loss, making your drive unrecognizable to Windows. If you dropped the drive or got it wet, the problem may be with the hardware.

Determining Logical or Physical Failure

Open the Disk Management tool to view all drives connected to your computer. If the drive is present in the list of connected media, then the problem is most likely logical. If the volume is listed with "unallocated space," this messsage means that Windows doesn't recognize the partitions on the drive, either because of a file-system error or an unsupported file system. Do not format the drive; doing so will erase the data. If the drive is not listed among unconnected devices, you probably have a hardware error. Hardware problems may be with the drive (or any drive-necessary cables) or the USB port on your computer. Test different USB ports to see if a different port solves the problem.

Drive Letter Conflicts

If the drive is present in Disk Management with a recognized file system (FAT or NTFS) but not in My Computer, you may have a problem with drive-letter conflicts. Right-click the external hard drive in Disk Management and select "Change Drive Letter and Paths." Choose a drive letter that is currently not in use from the drop-down menu. Check to see if this procedure makes the external drive appear in My Computer.

Use Another Computer

Connect your external drive to another computer. If you have used the drive on a computer with another OS, such OS X or Linux, connect it to that computer; it's possible that the drive was accidentally formatted into the Ext4 or HFS+ file systems, which WIndows cannot read. If another computer can read the drive, copy your files from the drive onto a compatible USB drive.

Data Recovery Software

If the drive appears in Disk Management, there's a good chance that the data is recoverable. Data recovery software such as Yodot, EaseUS and Pandora Recovery can recover files from a malfunctioning USB drive. Yodot and EaseUS both have the ability to recover partitions, which is likely the problem if your drive shows up as "Unallocated" in Disk Management.

Professional Data Recovery

If the information on the external hard drive is vital and you can't retrieve it on your own, the best course of action is to contact a professional data recovery service. These services are able to recover most data lost, whether the damage to the drive is physical or logical. While the success rate is high, these services are also quite a bit more costly than do-it-yourself data recovery software. Services like Salvage Data, Secure Data Recovery and DriveSavers allow you to mail your drives for processing.

Resources

About the Author

Ashley Poland has been writing since 2009. She has worked with local online businesses, supplying print and web content, and pursues an active interest in the computer, technology and gaming industries. In addition to content writing, Poland is also a fiction writer. She studied creative writing at Kansas State University.